The use of zinc compounds as a source for physiologically active zinc ions in oral care products such as mouthwashes, rinses and toothpastes is a widely accepted practice. Zinc has been used for its ability to neutralize oral malodor, and it is also recognized that zinc ions have antiplaque and anticalculus properties.
It is hypothesized that the mechanism of zinc ions in reducing calculus in dental applications is interference with two stages in the development of calculus, i.e., the structural formation of the plaque stage, and the mineralization of the plaque stage. Both of these stages normally make the plaque more cohesive, and therefore less permeable to penetration by the physiologically active chemical species in the oral environment. Zinc interferes with the attachment of the microbial elements to each other and to the mucilaginous matrix, and also can interfere with the calcification stage. In both stages the zinc ions function as an antagonist to calcium ions. It is postulated that a zinc compound, by preventing the plaque from becoming dense and strongly cohesive, causes permeability in the plaque which allows penetration by the physiologically active antiplaque and anticalculus ions in the oral environment.
Both water-soluble and water-insoluble zinc compounds have been utilized as physiologically active ingredients in oral care preparations. Water-soluble and highly ionized zinc compounds such as zinc chloride provide the best source of bioavailable zinc ions. However, zinc chloride in aqueous solution tends to form oxychlorides and zinc hydroxides of low solubility, which results in a two-phase cloudy solution.
The pH of a conventional zinc chloride solution can be lowered to less than 4.5 through the use of mineral or organic acid buffers to provide a stable and clear solution. However, this method is not acceptable since the resultant oral care product exhibits severe astringency and an undesirable metallic taste.
Zinc salts such as zinc phenolsulfonate as disclosed in U.S. Pat. No. 4,022,880, and zinc carboxymethylsuccinate, as disclosed in U.S. Pat. No. 4,144,323, tend to be stable at a higher pH than other zinc salts. Sparingly water-soluble salts such as zinc citrate have been used to moderate the release of zinc ions, thereby reducing astringency and providing a sustained level of in-vivo anticalculus activity. The use of various complexing agents such as sodium gluconate (U.S. Pat. No. 4,568,540), glycine (U.S. Pat. No. 4,339,432 and U.S. Pat. No. 4,425,325), sodium citrate, citric acid, and the like, have been employed for production of relatively stable solutions of zinc chloride.
The reaction or interaction of zinc compounds of varying solubility with anionic polymers containing carboxylic, sulfonic and/or phosphonic acid functionalities are described in U.S. Pat. No. 4,138,477.
U.S. Pat. No. 4,664,906 describes oral compositions containing hexedine and a zinc compound which exhibit antimicrobial activity. Opacified gel dentifrices are disclosed with contain sodium gluconate and a nonionic binder such as hydroxyethylcellulose.
U.S. Pat. No. 4,992,259 describes a clear aqueous composition of a zinc salt, a complexing agent such as succinic acid, and an anionic polymer such as sodium alginate.
Prior art of particular interest with respect to the present invention subject matter includes U.S. Pat. Nos. 4,022,880; 4,082,841; and 4,522,806. These references describe oral care products which contain a zinc compound and a polyamine compound as two of the formulation ingredients.
There is continuing interest in the development of new and improved oral care products which retard plaque and calculus formation in oral cavities.
Accordingly, it is an object of this invention to provide an oral care product which has superior properties for controlling oral malodor, plaque, calculus and gingivitis.
It is another object of this invention to provide an ingredient for oral care compositions which slow-releases bioavailable zinc ions in an oral cavity environment.
It is a further object of this invention to provide a clear single-phase aqueous solution of a normally water-insoluble zinc compound which has utility as an ingredient of improved palatability and reduced astringency in oral care compositions.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.